In hearing aids which fit into the user's ear, it is necessary to provide a vent from one end of the hearing aid to the other to relieve pressure which could otherwise build up in the ear canal behind the hearing aid. One method of producing such vents is shown in U.S. Pat. No. 4,569,812 issued Feb. 11, 1986 and assigned to Beltone Electronics Corporation. In that method a preliminary shell is formed and then tubing is placed within the preliminary shell. Then, additional liquid molding material is poured into the preliminary shell to form a final shell having a thick wall which covers the tubing. The tubing is then removed, producing a vent in the space which it formerly occupied.
Another and somewhat simpler method of producing a vent, which has been used by hearing aid manufacturers since at least 1982, has been to mold a conventional in-the-ear hearing aid shell of acrylic material and then to lay a piece of tubing against the interior wall of the shell. Acrylic molding material (the same as that from which the shell was made) is then brushed onto the tubing and is then cured. The tubing is then removed leaving a vent where the tubing was located.
A difficulty with both of the above methods is that interior space within the shell is extremely limited (since the shell must fit within the user's ear), and yet sufficient space is needed to house the hearing aid components, including the receiver, electronics, battery and controls. In both methods described above, a significant amount of space was occupied by the additional wall structure within the shell required to form the vent. In addition, both methods are highly labour intensive and costly.